Unique identifier

With reference to a given (possibly implicit) set of objects, a unique identifier (UID) is any identifier which is guaranteed to be unique among all identifiers used for those objects and for a specific purpose.

Types

There are three main types of unique identifiers, each corresponding to a different generation strategy:

• Serial numbers, assigned incrementally or sequentially
• Random numbers, selected from a number space much larger than the maximum (or expected) number of objects to be identified.
  • Although not really unique, some identifiers of this type may be appropriate for identifying objects in many practical applications and are, with abuse of language, still referred to as "unique"
  • See Hash table
• Names or codes allocated by choice which are forced to be unique by keeping a central registry such as the EPC Information Services.

The above methods can be combined, hierarchically or singly, to create other generation schemes which guarantee uniqueness.

Multiple unique identifiers per object

In many cases, a single object may have more than one unique identifier, each of which identifies it for a different purpose.

Relational databases

In relational databases, certain attributes of an entity that serve as unique identifiers are called primary keys.

See also

• Idempotence
• Identification scheme
• Identifier
• Relational database
• Serial code
• Set (mathematics)

External links

• Unique identifier @ Wikipedia